The proposed research deals with quantitative analysis of single first, second and third order mechanoreceptor neurons, comparing the properties of those neurons belonging to the "anterolateral" and "lemniscal" systems and relating these data to sensory discrimination in normal subjects and patients with anterolateral cordotomies for the relief of pain. In addition to the study of low threshold mechanoreceptors we plan to characterize the transformation of slowly conducting "nociceptor" fiber information at medullary and thalamic levels by analyzing the appropriate portions of the sensory trigeminal nuclear complex and the thalamic tactile regions in normal animals and after chronic sections of the dorsal columns and dorsolateral tracts. The latter studies should define ascending pathway to thalamic integration of somatosensory information. The quantitative data will be treated by various statistical methods including: curve fitting, information theory and incremental threshold analyses. Qualitative data will deal with attempts to discern patterns of modality segregation. Morphological studies of specific zones in the thalamic tactile region will be conducted by use to two tracer methods: One employing focal injection of tritiated leucine for subsequent tracing of axonal protein transport from tactile thalamus to cortex and from dorsal column nuclei and sensory trigeminal complex to thalamus and midbrain sites. The second series of studies employ retrograde axonal transport of horse radish peroxidase from tactile cortex to thalamic ventrobasal complex and from thalamus to dorsal column and trigeminal nuclei.